RFR: 8264130: PAC-RET protection for Linux/AArch64 [v2]

[Andrew Dinn]

On Wed, 10 Nov 2021 13:22:37 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Alan Hayward has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Simplify branch protection configure check
>
> src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 5185:
> 
>> 5183: // ROP Protection
>> 5184: 
>> 5185: void MacroAssembler::protect_return_address() {
> 
> We need proper, full, detailed comments about what these functions do, with reference to primary AArch64 documentation.

As far as the AArch64 docs are concerned the relevant details are provided in ARM-ARM D

- The PAC functionality is described in ARM-ARM Section D5.1.5
- Overview of the PAC instructions is provided in section C3.1.9
- Detailed PAC instruction descriptions are provided in C6.2.195 - C6.2.199

n.b. I am specifically referring to my (possibly out of date) copy ARM-DDI 0487D.a (ID103018) which is the Initial v8.4 EAC release from 2018.

That said, I agree that a description of how these functions use the underlying PAC support and what, effectively, they achieve via that usage would be necessary. A reference to the relevant sections of the ARM doc in the code would be helpful.

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PR: https://git.openjdk.java.net/jdk/pull/6334